The cytoplasmic domain of the integrin alpha4 subunit differs markedly from other alpha chain cytoplasmic domains with respect to focal adhesion formation, and this may account for increased cell migration but decreased cell spreading, adhesion strengthening, plasma membrane stiffness, and PIP4,5 synthesis. The principal investigator hypothesizes that distinctive structural features within the alpha-4 tail produce its specialized functions in coordination with specific biochemical associations and signaling pathways. Furthermore the principal investigator hypothesizes these unique features of the alpha-4 tail are critical in vivo for normal lymphocyte physiology and inflammation. To test this hypothesis he will: 1) evaluate alpha-4 tail mutants on blood cells in vivo; 2) use a panel of mutants to determine the exact tail residues responsible for migration, adhesion strengthening, coclustering with known cytoskeletal proteins and other specialized functions of the integrin alpha-4 tail; and 3) compare phosphoinositide synthesis and other signaling functions of wild type and mutant alpha-4 in K562 cells, CHO cells, and primary lymphocytes derived from RAG-2 chimeric mice. The use of minimal mutations with maximal functional effect will allow him to link conclusively alpha-4 specific positive and negative functional effects with specific colocalized proteins and specific signaling pathways Also he will have a unique opportunity to carry out definitive in vivo evaluations of the alpha-4 tail during normal blood maturation and during inflammation. The availability of primary mouse lymphocytes expressing mutant and wild type alpha-4 will allow an expanded analysis of alpha-4 specific signaling pathways.